The present invention relates to weighing systems and is concerned in particular with weighing systems utilizing a plurality of scales to achieve a minimum qualified weight from a selected combination of the scales.
Many products such as fruits, vegetables, candies and other small items are produced or manufactured with varying sizes and weights, and are handled in bulk quantities prior to being separated in groups and packaged. Combination weighing systems have been developed for selecting from a plurality of individual scales containing the product a particular combination of scales which cumulatively provides a total weight closely approximating or equaling the target or stated contents weight. Such weighing systems are described, for example, in U.S. Pat. Nos. 3,939,928 and 4,267,894.
Combination weighing systems have become more common through the advent of the microprocessor which is capable of sampling multiple combinations of scales in a very short period of time and determining which combination most satisfactorily provides a target weight. When the combination has been identified, those scales belonging to the combination are dumped into a common chute which discharges the collected product into a film wrapper or other container in a packaging machine. The process may be carried out repeatedly by a microprocessor with the scales reloaded or with the dumped scales eliminated from the search processes until they are reloaded.
The flexibility of microprocessors allows a multitude of scales to be examined during the search process and permits weight parameters to be readily adjusted in accordance with varying product and production demands. However, it is important that the weight information from each scale be accurate throughout extended periods of use and not be affected by drift in the components which process the weight information. For this reason, calibration systems are generally employed in the scale, and the systems are periodically activated to update the weighing parameters used by the processor.
Sampling of a weight in a given scale is frequently complicated by the environment in which the scales operate. Scales are commonly loaded from a vibrating feeder, and in order to isolate the scales and the weight measurement from the effects of the vibrator, resilient mounts support the critical measuring sensors and the scales. Nevertheless, spurious errors are introduced into the weight signals and produce inaccurate results in the final weight.
In spite of the speed with which microprocessors operate in comparison to the mechanical weighing devices, cycle times for performing the microprocessor functions are important because they are added to the sampling and reading times, and one microprocessor may service a number of scales which are loaded in staggered sets.
It is accordingly an object of the present invention to provide solutions to the problems mentioned above.